1. Field
The present teaching relates to a pattern forming method for forming a pattern on a substrate, and a method for producing a device using the pattern forming method.
2. Description of the Related Art
In order to enhance the resolution in an exposure apparatus which is used in the lithography step of producing a microdevice, an electronic device, etc. such as a semiconductor device or the like and which uses, for example, the ultraviolet light ranging from the far ultraviolet region to the vacuum ultraviolet region as the exposure light (exposure light beam), for example, the exposure wavelength has been shortened, the illumination condition has been optimized, and the liquid immersion method has been applied. Recently, in order to form a periodic circuit pattern having a pitch finer than the resolution limit of the exposure apparatus, the pitch-splitting process and the spacer double patterning process (Spacer transfer Process or Sidewall transfer Process) have been suggested. See, for example, Andrew J., Hazelton et al., “Double-patterning requirements for optical lithography and prospects for optical extension without double patterning”, J. Micro/Nanolith. MEMS MOEMS, (United States) Vol. 8 (1), 011003, January-March (2009).
The former pitch-splitting process is roughly classified into the double exposure process and the double patterning process. In the double exposure process, images of patterns of first and second masks having a pitch twice the device pattern to be finally formed are transferred to a nonlinear resist in such a state that the phases are deviated (shifted) from each other, and then the etching is performed. See, for example, H. Ohki et al., “Experimental study on non-linear multiple exposure method”, Proc. SPIE (United States) 3051, p. 85-93 (1997). In the double patterning process, a process such as the etching or the like is executed between the exposure with an image of a first mask pattern and the exposure with an image of a second mask pattern.
In the latter spacer double patterning process (spacer process method), for example, a plurality of line patterns having ¼ pitch are formed by performing the exposure and the development with an image of a mask pattern having a pitch which is twice the device pattern. A spacer is deposited on space portions (side wall portions) located on the both sides of the respective line patterns, for example, and then the respective line patterns are removed. Thus, the pattern having ½ pitch is obtained. See, for example, W. Jung et al., “Patterning with amorphous carbon spacer for expanding the resolution limit of current lithography tool”, Proc. SPIE (United States) 6520, 65201C (2007).